This invention relates to a method and apparatus for measuring the load limit of a load bearing member such as a beam, channel or other slender structure load bearing member. In particular, this invention provides a method and apparatus for directly and simply indicating the point at which a load bearing means such as a beam or channel reaches a pre-selected limit or amount of deflection or stress. The invention also includes means for producing a signal at the limit point which can be used to control or activate means to stabilize, reduce or relieve the stress or load on the structural member thereby preventing damage to the member and appurtenant apparatus.
The method and apparatus of this invention are rugged and simple and particularly applicable to use on well pumping units for oil or other normally liquid or easily liquified natural resources where simplicity, ruggedness and reliability are of prime importance. These advantages are the result of an apparatus which can be constructed of numerous, readily available materials and which has only two portions which move in relation to each other and which in several preferred embodiments has no parts requiring close tolerance fitting or moving parts. In one preferred embodiment a sensor means does provide slideably adjustable sensor or contact points fitted within an insulating sleeve.
The deflection or load limit indicator of this invention is particularly useful with pumps such as pumping units used on oil wells which have a reciprocating length of sucker rod pumping means disposed in the well bore with valve means which lifts liquids or slurry of liquids with some solids and/or gas from the well upon reciprocation. The sucker rods and slurry are supported from the end of a beam or load bearing means which is pivoted about an axis or bearing attached near the middle or end opposite the sucker rods to a supporting means such as a frame or cross beam supported by a frame. The load bearing means, called a walking beam, is pivoted or reciprocated about the axis by a driving means such as an electric or internal combustion motor attached to the walking beam through a reciprocating means such as a crank shaft and pitman arm or beam. The walking beam or driving means typically has a weight and/or load balancing means to adjust the maximum load portion of the pumping cycle and weight and/or force distribution on the beam and drive means. The walking beam also typically has a constant radius head called a horse head from which the sucker rods are supported to provide constant vertical pull on the rods. The load adjustable components of the pumping unit make it difficult to use any conventional load or stress limit apparatus or method due to the changing load conditions during each cycle and over a period of time as the condition of the pumping unit, sucker rods and liquid slurry changes. This is especially applicable in oil fields using water flooding or where the slurry contains a large portion of water or aqueous fluid such as field brine where the load of the slurry column in the well bore can drastically change the load on the pumping unit.
This invention can be attached directly to the walking beam of the pumping unit, usually either on top or the bottom, even in the field after the pumping unit is in service to directly measure or indicate the point at which the load or deflection of the beam reaches a pre-selected limit. The deflection or load limit indicator of this invention produces a signal when the limit is reached which can be used to stop the pump or decrease the stress or deflection to prevent damage to the pumping unit.